Latitudinal and longitudinal dispersion of energetic auroral protons

International audienceUsing a collision by collision model from Lorentzen et al., the latitudinal and longitudinal dispersion of single auroral protons are calculated. The proton energies varies from 1 to 50 keV, and are released into the atmosphere at 700 km altitude. The dipole magnetic field has a dip-angle of 8 degrees. Results show that the main dispersion region is at high altitudes (300-350 km) and occurs during the first few charge exchange collisions. As the proton travels further down the atmosphere the mean free path becomes smaller, and as a result the spreading effect will not be as pronounced. This means that the first few charge exchange collisions fully determines the width of both the latitudinal and longitudinal dispersion. The volume emission rate was calculated for energies between 1 and 50 keV, and it was found that dayside auroral hydrogen emissions rates were approximately 10 times weaker than nightside emission rates. Simulations were also performed to obtain the dependence of the particle dispersion as a function of initial pitch-angle. It was found that the dispersion varies greatly with initial pitch-angle, and the results are summarized in two tables; a main and an extreme dispersion region

Cost evaluation of mitigation strategies for injectivity challenges- a scenario analysis

Global warming is a key concern for human society and anthropogenic emissions must be reduced. To aid this development, carbon capture and storage has showed a great potential. Here, carbon dioxide is captured and stored in geological formations. Until now, economic profitability of this technology has been limited to the oil and gas industry. Here, the CCS technology is more easily implemented as the investment and operating cost can be justified with the high carbon dioxide tax, infrastructure and reservoir knowhow. Outside of the hydrocarbon industry, the startup phase of any CCS project will require high initial investment in regard to capture facilities, transporting infrastructure, terminal and storage sites. To compensate for these expenditures, substantial volumes of CO2 must be injected into the subsurface. The Northern Lights project is the world’s first full scale carbon capture and storage development with third-party customers. In this large-scale project profitability will be generated by obtaining a high injection rate. To ensure technical feasibility, multiple geological studies have been performed; however, CO2 has not yet been injected into the formation. Therefore, the possibility of unforeseen geological events rises. When CO2 is injected to the storage site, geochemical interactions are imposed. The reactions can alter the rock properties, causing lower injection rates. Experience from CCS operations like the Norwegian Snøhvit and Sleipner project, which were salt precipitated and sand influx respectively, has proven that geochemical interactions can have fatal consequences. In this thesis three different scenarios are developed to investigate the economic outcomes of injectivity reduction in the storage formation of the Northern Lights project. The scenarios are build based on previous injectivity challenges, and geochemical simulations. The simulations were performed using the PHREEQC software to model the behaviour of different mineral in the Aurora formation. Simulation showed a large amount of calcite precipitating that can potentially clog the wellbore region. Moreover, to calculate the economic outcomes a pre-tax present value analysis with data from open access sources was performed. The scenarios investigated in this study shows that a 10 % reduction in well injectivity increases storage cost with 51 % whereas in scenarios where mitigation measures are conducted the cost increase is between 4-30 %. This thesis indicated that preparing for injectivity problems is more favourable in terms of limiting the cost of storage, although upfront investment of mitigation measures might seem substantial

On the contribution of thermal excitation to the total 630.0 nm emissions in the northern cusp ionosphere

Direct impact excitation by precipitating electrons is believed to be the main source of 630.0 nm emissions in the cusp ionosphere. However, this paper investigates a different source, 630.0 emissions caused by thermally excited atomic oxygen O$(^{1}$D) when high electron temperature prevail in the cusp. On 22 January 2012 and 14 January 2013, the European Incoherent Scatter Scientific Association (EISCAT) radar on Svalbard measured electron temperature enhancements exceeding 3000 K near magnetic noon in the cusp ionosphere over Svalbard. The electron temperature enhancements corresponded to electron density enhancements exceeding $10^{11}$m$^{-3}$ accompanied by intense 630.0 nm emissions in a field of view common to both the EISCAT Svalbard radar and a meridian scanning photometer. This offered an excellent opportunity to investigate the role of thermally excited O$(^{1}$D) 630.0 nm emissions in the cusp ionosphere. The thermal component was derived from the EISCAT Radar measurements and compared with optical data. For both events the calculated thermal component had a correlation coefficient greater than 0.8 to the total observed 630.0 nm intensity which contains both thermal and particle impact components. Despite fairly constant solar wind, the calculated thermal component intensity fluctuated possibly due to dayside transients in the aurora

Heun Functions and the energy spectrum of a charged particle on a sphere under magnetic field and Coulomb force

We study the competitive action of magnetic field, Coulomb repulsion and space curvature on the motion of a charged particle. The three types of interaction are characterized by three basic lengths: l_{B} the magnetic length, l_{0} the Bohr radius and R the radius of the sphere. The energy spectrum of the particle is found by solving a Schr\"odinger equation of the Heun type, using the technique of continued fractions. It displays a rich set of functioning regimes where ratios \frac{R}{l_{B}} and \frac{R}{l_{0}} take definite values.Comment: 12 pages, 5 figures, accepted to JOPA, november 200

The influence of engine demand map design on vehicle perceived performance

This paper reports a study into the influence of the steady state engine demand map on perceived performance. Analysis of the results of a survey of 24 C and C/D class 1600cc cars is presented and shows that the primary parameters are mean wide-open throttle acceleration, throttle progression, and part-throttle rate of change of acceleration with engine speed. These results are used to design a factorial experiment to investigate these parameters using an electronic throttle system. This approach eliminates problems of inter-vehicle variations in noise, comfort or general image, allowing subjective ratings to be attributed directly to the demand map changes. The results are discussed in terms of the significant main effects and interactions and as response surfaces, from which optimum setups can be determined

On the possible role of cusp/cleft precipitation in the formation of polar-cap patches

International audienceThe work describes experimental observations of enhancements in the electron density of the ionospheric F-region created by cusp/cleft particle precipitation at the dayside entry to the polar-cap convection flow. Measurements by meridian scanning photometer and all-sky camera of optical red-line emissions from aurora are used to identify latitudinally narrow bands of soft-particle precipitation responsible for structured enhancements in electron density determined from images obtained by radio tomography. Two examples are discussed in which the electron density features with size scales and magnitudes commensurate with those of patches are shown to be formed by precipitation at the entry region to the anti-sunward flow. In one case the spectrum of the incoming particles results in ionisation being created, for the most part below 250 km, so that the patch will persist only for minutes after convecting away from the auroral source region. However in a second example, at a time when the plasma density of the solar wind was particularly high, a substantial part of the particle-induced enhancement formed above 250 km. It is suggested that, with the reduced recombination loss in the upper F-region, this structure will retain form as a patch during passage in the anti-sunward flow across the polar cap